Patent CA-2641704-A1 (CA)
Title: Laser interferometric accelerometer
Inventor: ERDMANN ERICH
IPC: G01P15/00
Filed: 2008-09-29
Abstract: The reason for our invention is a more foolproof system then the conventional mechanical systems. It is a well known fact that mechanical devices and instruments in a stressful environment are much more likely to breakdown then none mechanical ones for such reasons that they have no moving parts in them. To give an example, air driven mechanical gyroscopes in airplanes occasionally do malfunction and that is why some airline corporations have switched to using laser gyros. The principle of the laser gyro is not new, but was invented in 1913 by Carl Sagnac. The invention of the laser has made it possible to produce a device that can be used in airplanes. Likewise we feel that our Laser Interferometric Accelerometer is also more reliable then conventional systems and should be made use of as well.   The Laser Interferometric Accelerometer is a none mechanical device that operates on the principle of an interference pattern generated by the convergence of two beams of monochromatic light, which have been generated from a single beam, by first passing the light through a beam splitter, after which one beam passes through a glass prism and the other beam passes through air or a vacuum after that they form a single beam again and the interference lines can be viewed in a regular eyepiece such as used in a telescope. The monochromatic light can be produced by regular white light passed through a narrow band filter or from a laser or an inexpensive laser diode, which works also quite well.   The Laser Interferometric Accelerometer makes use of two basic principles. The first is based on the Doppler effect where the monochromatic light can shift from its original colour either towards the blue or towards the red. Doppler had actually discovered this effect while walking along the track with his little daughter who asked him what caused the pitch change in the train's whistle as it passed by. The accelerometer is so oriented in the plane or space vehicle that the beam is pointing in the direction of motion. Due to the fact that light is not instantaneous, but takes time from its source to reach the detector, it will be red shifted by the time it reaches the detector due to the fact that moment by moment the accelerating vehicle moves with ever greater speed. Once the desired speed has been reached the light will not be red shifted anymore.   The second principle involved is based on the fact that light moves slower through glass than air or a vacuum. The beam of light passing through glass takes longer although the glass portion is physically the same length as the beam of light through the air, as a result through the glass the light is even more red shifted then the beam of light passing through air. When both beams of light are recombined an interference pattern drift will show up due to the fact that the light in one light beam is more red shifted than the light in the other. An electronic counting device attached to a photo detector can be used to calculate and display the number of the interference pattern bar drift on a computer screen.   We feel that in space travel G force measurements due to acceleration are vital primarily for the safety of the astronauts, our device could have an application there, being that it is none mechanical and inexpensive to manufactur.